Cell with NiCl2 cathode

ABSTRACT

A non-aqueous electrochemical cell having an alkali or alkaline earth metal anode, an inorganic electrolyte comprised of an electrolyte salt and sulfur dioxide and a cathode comprised of NiCl 2 .

This invention relates to non-aqueous sulfur dioxide containingelectrochemical cells and more particularly to such cells containinginorganic sulfur dioxide electrolytes.

It has recently been discovered that a factor involved in making viablerechargeable cells has been the elimination of the normally requisiteorganic cosolvents from cells containing sulfur dioxide (SO₂). Theorganic cosolvents as well as most other organic materials tend to beinvolved in generally irreversible reactions whereas ideallyrechargeable cells require substantially complete reversibility of thecomponents. However, such elimination of organic cosolvents hasnecessitated the utilization of electrolyte salts which are both solublein the SO₂ alone (a generally poor solvent) and which provide autilizable conductive electrolyte solution. An additional factor is thevery high cost of some of the salts which may be used in this respect.Salts such as tetrachloroaluminates, tetrachlorogallates,tetrachloroindates as well as clovoborates of the alkali or alkalineearth metals were found to be useful in SO₂ alone (clovoborates are,however, very expensive). In such cells it is feasible to effectivelyutilize the SO₂ as only a solvent in the cell by using a solid cathodeactive material. However, not all solid cathode active materials providea cell capacity which compares favorably with the capacity of a cellhaving the SO₂ as the cathode active materials. In fact it has beennearly impossible to predict with any certainty which cathode activematerials are of utility in inorganic SO₂ cell environments. Thus, forexample, different halides of the same metal, though normally equated interms of function, have been shown to have markedly different propertiesparticularly in the inorganic SO₂ cell environment.

It is an object of the present invention to provide a cathode activematerial for use in a non-aqueous SO₂ containing cell, particularly inan inorganic SO₂ containing cell which provides a high cell capacity.

This and other objects, features and advantages of the present inventionwill become more evident from the following discussion.

Generally the present invention comprises an electrochemical cell havingan alkali or alkaline earth metal anode, preferably lithium, includingmixtures and alloys thereof, an electrolyte comprised of SO₂, and anelectrolyte salt soluble in SO₂ and a cathode comprised of NiCl₂. Theelectrolyte is preferably inorganic for rechargeable cell purposes. TheNiCl₂ has been discovered to be a useful cathode material despite thefact that NiF₂ (a halide analogue thereof) provides a relatively lowdischarge capacity.

The NiCl₂ cathode active material is preferably admixed with aconductive material such as graphite or carbon black in amounts rangingfrom 10-30% by weight thereof and a binder such aspolytetrafluoroethylene (PTFE) in amounts between about 5-15%.

The electrolyte salts useful in the present invention include alkali andalkaline earth metal halide salts of aluminum, tantalum, niobium,antimony, gallium, indium and clovoborates which are insoluble in SO₂,particularly those having the anions AlCl₄ ⁻, TaCl₆ ⁻, NbCl₆ ⁻, SbCl₆ ⁻,SbCl₆ ⁻³, GaCl₄ ⁻, InCl₄ ⁻, B₁₀ Cl₁₀ ⁻² and B₁₂ Cl₁₂ ⁻². The salts areutilized by dissolving them in the SO₂ in low concentration; i.e., about1 molar, or, as described in copending application Ser. No. 405,980,they may be present in high concentrations with SO₂ in a mol equivalentratio no greater than 1:7. Preferably, the SO₂ electrolyte is inorganic.

In order to more fully illustrate the present invention the followingexamples including comparisons with non-operable materials arepresented. It is understood that such examples are for illustrativepurposes and that details contained therein are not to be construed asbeing limitations on the present invention. Unless otherwise indicatedall parts are parts by weight.

EXAMPLE 1

A cell is made with about 20 gms of a LiAlCl₄.3SO₂ (mole equivalentratio) electrolyte, two lithium electrodes with each having a copperfoil substrate and having the dimensions 2.5×4.1×0.05 cm and a 1.4 gmcathode between the lithium electrodes comprised of 80% NiCl₂, 12%carbon black (Ketjenblack EC from Noury Chemical Corp.) and 8% PTFE on anickel grid. The cathode has the dimensions 2.5×4.1×0.13 cm and isseparated from the lithium electrodes by non-woven glass separators. Thecell is discharged at 20 mA and provides a capacity of 700 mAhr to a 1volt cutoff and an OCV of 3.15 volts. The obtained capacity is about303% of the theoretical capacity of NiCl₂.

EXAMPLE 2

A cell is made as in Example 1 but with an electrolyte of 1M LiAlCl₄ inSO₂. The obtained OCV is 3.1 volts and at 20 mA discharge provides acapacity of 340 mAhrs to a 1 volt cutoff. The obtained capacity is about147% of the theoretical capacity of NiCl₂.

EXAMPLE 3

A cell is made as in Example 1 but with a 1M LiGaCl₄ in SO₂ electrolyte.The obtained OCV is 2.9 and at a 20 mA discharge rate provides acapacity of 546 mAhrs to a 1 volt cutoff. The obtained capacity is about237% of the theoretical capacity of NiCl₂.

EXAMPLE 4 (COMPARATIVE)

A cell is made as in Example 1 but with a 1.7 gm cathode containing NiF₂with a thickness of 0.12 cm. The cell provides a OCV of 3.2 volts andwhen discharged at 20 mA provides a capacity of 320 mAhrs to a 1 voltcutoff. The obtained capacity is about 84.5% of the theoretical capacityof the NiF₂.

EXAMPLE 5 (COMPARATIVE)

A cell is made as in Example 4 but with a 1M LiGaCl₄ in SO₂ electrolyte.The cell provides an OCV of 2.96 volts and at a discharge rate of 20 mAprovides 284 mAhrs. The obtained capacity is about 75% of thetheoretical capacity of the NiF₂.

It is evident from the above examples that NiCl₂ provides at least fourtimes the capacity of an analagous NiF₂ cathode under identicalconditions and with various inorganic SO₂ containing electrolytes.

It is understood that the above examples are for illustrative purposesand that the present invention is not to be limited to the specificscontained therein. Changes including those involved in cellconstruction, components and ratios may be made without departing fromthe scope of the present invention as defined by the following claims.

What is claimed is:
 1. A non-aqueous, electrochemical cell comprising ananode comprised of an alkali or alkaline earth metal and an inorganicelectrolyte comprised of SO₂ with an electrolyte salt dissolved therein,characterized in that said cell contains an active cathode comprised ofat least 55% by weight of NiCl₂ NiCl₂ admixed with a conductive carbonmaterial with said conductive carbon material comprising from 10-30% byweight of said cathode.
 2. The cell of claim 1 wherein said electrolytesalt is selected from the group consisting of alkali or alkaline earthmetal clovoborates and alkali and alkaline earth metal halide saltscontaining gallium, indium, aluminum, tantalum, niobium, or antimony. 3.The cell of claim 2 wherein said electrolyte salts are lithium salts. 4.The cell of claim 1 wherein said anode is comprised of lithium.
 5. Thecell of claim 1 wherein said electrolyte salt is selected from the groupconsisting of LiAlCl₄ and LiGaCl₄.
 6. The cell of claim 1 wherein saidsalt is LiAlCl₄.
 7. The cell of claim 6 wherein the more equivalentratio of LiAlCl₄ to SO₂ is no greater than 1:7.
 8. A non-aqueous,electrochemical cell comprising a lithium anode and an inorganicelectrolyte comprised of SO₂ and LiAlCl₄, characterized in that saidcell contains an active cathode comprised of at least 55% by weight ofNiCl₂ NiCl₂ admixed with a conductive carbon material with saidconductive material comprising from 10-30% by weight of said cathode. 9.The cell of claim 8 wherein the mole equivalent ratio of LiAlCl₄ to SO₂does not exceed 1:7.
 10. A non-aqueous, electrochemical cell comprisinga lithium anode and an inorganic electrolyte comprised of SO₂ andLiGaCl₄ characterized in that said cell contains an active cathodecomprised of at least 55% by weight of NiCl₂ NiCl₂ admixed with aconductive carbon material with said conductive carbon materialcomprising from 10-30% by weight of said cathode.